5 96 THE HISTORY OF BIOLOGY 



which has been both contradicted and supported by others, that the cellular 

 membranes consist of a peculiar category of elements called lipoi-ds^ elements 

 dissolved in these permeate the cell-v/alls, and vice versa. 



Ferment chefnistry 

 With colloid chemistry the modern chemistry of ferments is closely allied. 

 In regard to ferments it has been known for a hundred years that through 

 their presence in extremely small quantities they are capable of causing vari- 

 ous chemical changes in large masses of the substances on which they are 

 acting. In modern times this influence they exert has been compared with 

 the catalytic effect of certain inorganic substances (first pointed out by Ber- 

 zelius), as, for instance, the part played by acid in the production of ether 

 out of alcohol. Of fundamental importance is the discovery that not only 

 are phenomena of disintegration induced by ferments, but also synthetic 

 processes, as, for example, the production of starch in the leaves of plants 

 through the chlorophyll granules under the influence of sunlight. The fer- 

 ment syntheses of fats, albuminous substances, and other products of vege- 

 table and animal life, which have been the objects of special study, are in 

 themselves of immense interest, but they cannot be discussed in detail here; 

 nor can we describe the extremely subtle investigations that have been carried 

 out in connexion with the co-operation of various ferments within the same 

 vital unit. 



In connexion with fermentation research mention should be made of 

 the process of internal secretion, our knowledge of which has increased more 

 and more in recent times. Bernard, whom we mentioned earlier, may claim 

 to have been its discoverer. As we have seen, it was he who established the 

 fact that the liver produces substances which are directly carried away by 

 the blood. Charles Edouard Brown-Sequard (1817-94) succeeded to Ber- 

 nard's professorship after the latter's death. The son of an American father 

 and a French mother, Brown-Sequard studied at Paris and afterwards worked 

 in England and America, but later on returned to France. He became fa- 

 mous for his valuable investigations in the sphere of neuro-physiology, but 

 more especially for his experiments, which he published in his old age, with 

 the injection of extract of genital glands, whereby he demonstrated that 

 these glands contain a special secretion inducing sexual desire. The experi- 

 ments in themselves were somewhat clumsy and were published with a good 

 deal of advertisement, especially as regards the power of rejuvenating the 

 individual, which was promised as a result of them; all the same, it cannot 

 be denied that through them attention was drawn to a fact that has since 

 been investigated by others with greater thoroughness than before. The in- 

 terstitial gland of the genital organs has been anatomically investigated by 

 the two collaborators Ancel and Bouin, of Nancy; its physiological func- 

 tion and, in general, the influence of the genital organs upon the vital 



