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departments are not desirous of limiting the output of new knowledge from 

 their laboratories by insisting on the wider training for the men of science who 

 are in the process of developing as students of research. 



It is perhaps true, also, that there still remains a great deal unobserved or 

 unrecorded in the fields of biology, physiology, and biochemistry, in the investiga- 

 tion of all of which a broad training is not specially required to give good 

 service ; and that, further, this condition will obtain for one or two decades still. 

 It is quite as certain, however, that the returns from such service will tend to 

 diminish in number and value, and, if the coming generation of workers is not 

 recruited from a systematically and broadly trained class of students, a period 

 of comparative sterility may supervene. 



As it is to-day, there are few who devote themselves to the direct study of 

 the chemical and physical properties of the cell, the fundamental unit of living 

 matter. There are, of course, many who are concerned with the morphology of 

 the cell, and who employ in their studies the methods of hardening and staining 

 which have been of very great service in revealing the structural as well as the 

 superficial chemical properties of the cell. On the facts so gained views are 

 based which deal with the chemistry ox the cell, and which are more or less 

 widely accepted, but the results and generalisations drawn from them give us 

 but little insight into the chemical constitution of the cell. We recognise in the 

 morphologists' chromatin a substance which has only in a most general way an 

 individuality, while the inclusions in the nucleus and the cytoplasm, on whose 

 distinction by staining great emphasis is laid, can only in a most superficial way 

 be classified chemically. 



The results of digestion experiments on the cell structures are also open to 

 objection. The action of pepsin and hydrochloric acid must depend very largely 

 on the accessibility of the material whose character is to be determined. If 

 there are membranes protecting cellular elements, pepsin, which is a celloid, if 

 it diffuses at all, must in some cases at least penetrate them with difficulty. In 

 Spirogyra, for example, the external membrane formed of a thick layer of 

 cellulose is impermeable to pepsin, but not to the acid ; and, in consequence, the 

 changes which occur in it during peptic digestion are due to the acid alone. 

 Even in the cell whose periphery is not protected by a membrane, the insoluble 

 colloid material at the surface serves as a barrier to the free entrance of the 

 pepsin. It is, however, more particularly in the action on the nucleus and its 

 contents that peptic digestion fails to give results which can be regarded as free 

 from objection. Here is a membrane which during life serves to keep out of the 

 nucleus not only all inorganic salts but also all organic compounds, except chiefly 

 those of the class of nucleo-proteins. That such a membrane may, when the 

 organism is dead, be permeable to pepsin is at least open to question, and in 

 consequence what we see in the nucleus after the cell has been acted on by 

 pepsin and hydrochloric acid cannot be adduced as evidence of its chemical or 

 even of its morphological character. 



The results of digestive experiments on cells are, therefore, misleading. 

 What may from them appear as nucleo-protein may be anything but that, while, 

 if the pepsin penetrates as readily as the acid, there should be left not nucleo- 

 protein, but pure nucleic acid, which should not stain at all. 



The objections which I now urge against the conclusions drawn from the results 

 of digestion experiments have developed out of my own observations on yeast cells, 

 diatoms, Spirogyra, and especially the Blue-green Algae. The latter are, as is 

 Spirogyra, encased in a membrane which is an effective barrier to all colloids. 

 When, therefore, threads of Oscillaria are subjected to the action of artificial 

 gastric juice, a certain diminution in volume is observed owing to the dissolving 

 power of the hydrochloric acid, and an alteration of the staining power of certain 

 structures is found to obtain ; but the pepsin has nothing to do with these, as may 

 be determined by examination of control preparations treated with a solution 

 of hydrochloric acid alone. 



It is thus seen how slender is our knowledge of the chemistry of cells derived 

 from staining methods and from digestion experiments. That, however, has not 

 been the worst result of our confidence in our methods. It has led cytologists 

 to rely on these methods alone, to leave undeveloped others which might have 

 thrown groat light on the chemical constitution of the cell, and which might have 



