against the workers and for the bosses.' In another 36 there is a catechism which begins:

'Did Jesus come from heaven?' 'No.' 'Was his mother a virgin?' 'No.'

'Is the story about him true?' 'No.'

Who was his father?' 'Joseph, just in the ordinary way.' 'Thus the story is a legend?' 'Of that there is no doubt.'

As one who has long been engaged in the education of boys, I denounce, in the strongest terms, these attempts to set boys of one class against those of another class, fostering hatred where love should reign, and preaching atheism instead of faith. Under the guise of social progress, the Communist Party is attempting to corrupt the youth of the nation, and I shall feel proud if this article helps to arouse general indignation against those who are steadily doing the devil's work. Let us remember our Lord, who took a little child and set him in the midst of them, and said: 'Whoso shall offend one of these little ones which believe in Me, it were better for him that a millstone were hanged about his neck, and that he were drowned in the depth of the sea.'

36 Proletcult for October 1923.

J. A. NAIRN.

AS A BIOLOGIST SEES IT

THERE is no world but one world, and every man is its prophet. Yet as each of us can be but the prophet of the small part of which he has experience, in effect we are in the position that each man has a world of his own. The natural insistence of man upon his own point of view must be my excuse for obtruding here a biologist's outlook.

In speaking of the world, whether that of the poet, the biologist, or of the philosopher, I am of course speaking of that symbolical world which exists in thought of the peculiar propaganda which each of us feels called upon to push in order to escape the charge of stultifying his own existence. And as most of us are probably agreed that thought is a function of man, the understanding of the human material is a matter of some importance. For not only does thought emanate from this material, but, through percolation, it reacts upon it to produce what is generally termed progress. But whether as concerned with the production of thought or of its reactions towards thought, it is with the nature of the material that we have to do. That this material is in a marked degree heterogeneous was probably recognised long before human records existed. There has always been the question as to how far this heterogeneity was dependent upon surrounding circumstances, and how far upon the inherent nature of the material itself. The recent outburst of experimental work upon heredity has led the biologist to lay increasing stress upon the latter factor, and to emphasise the importance of nature as opposed to nurture. New methods have enabled us to analyse the living thing in a way undreamt of a few years ago. The most distinguished of American geneticists has told us that the problem of heredity is solved; and though some of us deem the statement over-sanguine, it must be conceded that it may nevertheless be true. A few years' more work are necessary to tell us whether certain apparently unconformable cases are in reality essentially different, or whether they will ultimately fall into line with those already worked out in such detail.

If such should prove to be the case, what exactly does this solution' mean? Neither more nor less than a clear conception

of the mechanism by which the qualities of one generation are passed over to the next. It does not necessarily entail any understanding of these qualities in respect of their chemical or physical basis. Nevertheless our conception of their nature must of necessity be limited by our knowledge of the mechanism through which they are transmitted. The more precise our knowledge of the machinery, the more clearly can we envisage the nature of the material with which it can adequately deal. If, with the majority of biologists to-day, we look upon the chromosomes contained in the cell as the physical basis of heredity, and if we regard the peculiar phenomena presented by these bodies in the formation of the germ-cells as expressive of the mechanism by which are distributed the factors corresponding to definite qualities, then we are led to draw certain inferences as to the nature of these factors.

In the first place they must be very small. The chromosomes themselves are minute. They vary, of course, very much in size. The larger are naturally more comfortable to work with, and the cytologist would probably consider himself fortunate if he had to work with those of such magnitude that only a million went to the millionth part of a cubic inch. Small as are the chromosomes, the transmissible factors must be very much smaller. The American school has brought forward evidence for supposing that more than fifty may be contained in a single chromosome, and there is little doubt that, with further analysis, this number will be added to. That a limit will eventually be reached is indicated by the fact that more factors have been identified with the larger than with the smaller chromosomes.

We may take it then that the factor, the something that in the germ-cell corresponds to a given quality in the individual, is ultra-microscopic in size, and perhaps of the order of the larger chemical molecules. Minute, however, as it must be, the facts of transmission force us to believe that it is a perfectly definite thing; for in its passage through the mechanism it preserves its integrity. The factor that in a rabbit gives rise to black as opposed to white will continue to be transmitted in its entirety, no matter how often the black is crossed with white. It goes through the mechanism again and again, and again and again it gives rise to the same result, viz., black. There is no reason for supposing that it undergoes alteration as the result of repeated distribution.

Lastly, these postulated factors must be capable of reproduction of their like. A single sperm of a black buck mated to a white doe contains the factor that brings about the development of his son's black coat. And not only is his son's coat black, but 50 per cent. of that son's germ-cells also contain the 'black

factor. Hence we must suppose that the black factor augments in quantity with each successive cell division in which the chromosome containing it takes part. It is living matter in so far as it possesses the property of continuous growth.

To sum up, our factors must be regarded as exceedingly minute but definite bodies, having relative permanence, and with the capacity for reproducing their like. It may be remarked that, after all, they are not so very different from the 'physiological units' of Spencer, the 'gemmules' of Darwin, or the 'biophors' of Weismann. This is true. Nevertheless the discovery of the nature of the hereditary mechanism gives to the conception of such particles a higher validity than heretofore.

Given our factors, then, there are two questions that force themselves upon us: What is their nature? and How far can they be held accountable for the qualities of the living thing? In the former we are asking whether we can identify our factor with anything in the experience of the chemist, and ultimately of the physicist. Though we cannot say that much progress has been made in this direction, there are indications of a close relation between the factor and the chemist's enzyme, a relationship in some cases so close as to suggest identity. In the disease known as alkaptonuria the urine becomes dark after exposure to air, owing to the arrest of the normal breaking down of the nitrogenous products at a stage precedent to the formation of urea. It is the oxidation of this antecedent to urea-homogentisic acid -that leads to the darkening of the urine in alkaptonuric patients. Now the transition from homogentisic acid to urea is dependent upon the action of a specific enzyme. The natural inference is that alkaptonuric people lack this enzyme. But the alkaptonuric `state behaves as a Mendelian recessive to the normal, and we therefore suppose that the normal contains a factor which the former lacks. The genetic evidence, taken with the chemical, clearly points to the identity of a hereditary factor with an enzyme-producing substance, if not with the enzyme itself. Moreover, we are now acquainted with other examples, both in plants and animals, which point to an equally close connection between the factor and the enzyme.

It is not suggested that a living organism is merely a collection of enzymes. Clearly there must be some stuff for these to work upon. But it is possible that the waste products elaborated by one enzyme may be the stuff upon which another enzyme works later on in the sequence of life changes. Stuff, it is true, we must have in the beginning, but this may be provided by the original substance of the ovum, inert of itself, but under a series of enzyme reactions, initiated either by a spermatozoon, or by some other stimulus as in artificial parthenogenesis, producing in orderly

sequence the various products that go to make the living body. What that sequence is we can readily see, but the manner of its control is at present beyond us. It may be that the by-products of one enzyme reaction give, as it were, the signal to the next to come into action-that the life of the individual is a series of chemical reactions, preordained when the ovum was fertilised by the sperm. Or it may be that some other form of control dictates the manner in which the hereditary factors eventually find expression in the qualities of the organism. But whatever light future research may throw upon the mechanism of development, we have at any rate some knowledge of the mechanism of heredity. For we have established a genetic relation between the beginning and the end terms-between the factor as it exists in the germ-cell and the character as it manifests itself in the individual.

And this brings us to our second question-How far are all qualities dependent upon genetic factors? It is to try and answer this question that most of the genetic work of the past twenty years has been carried out. Anyone surveying the field from the early days of Mendelian research, when only the very simple cases were capable of analysis, cannot fail to be struck with the enormous progress that has been made. The rapid growth in the technique of analysis enables us to-day to attack problems which ten or fifteen years ago seemed almost insoluble. Given comparatively few facts, the geneticist can often suggest at once a reasonable and plausible interpretation, in much the same way as the older anatomists were able to make an approximate reconstruction of a whole animal from a few odd bones. Such interpretations are naturally put to the test of experiment before being admitted into the corpus of genetic knowledge.

We may, however, to-day claim that, in view of the variety and number of qualities proved to be inherited on a factorial basis, there are good grounds for supposing that all hereditary qualities are on the same basis, and are capable of interpretation in terms of genetic factors. A given quality of course cannot always be interpreted in terms of a single factor, and the fact that such cases bulk largely in the text-books is due to the ease with which they can be analysed, and the facility with which they lend themselves to purposes of demonstration. But careful analysis has already been made of qualities of which the manifestation is dependent upon the interaction of two, three, or even four factors, and there is little doubt that as time goes on even more complex cases will be expressed in terms of hereditary factors. But, whatever the number of factors concerned, the principle remains the same, and we have yet to find heritable qualities which cannot be expressed in terms of relatively few genetic factors.

The world of the biologist, therefore, is a world to be inter