MODERN BIOLOGY 539 



by fission, and that build up those structures of which the cell is composed. 

 These ultra-microscopical particles, which therefore cannot be observed, 

 but the assumption of which he considers to be an incontrovertible neces- 

 sity, he calls "plasomes." It is not worth while going further into his spec- 

 ulations; it will at once be realized that we here have a name for Haeckel's 

 plastidules, Darwin's gemmules, and innumerable similar ideas — unknown 

 quantities that can be used neither for the purposes of observation nor for 

 theoretical calculation and that are therefore automatically eliminated from 

 the problem of life. True, ultra-microscopical technics have since given us 

 some insight into the composition of the living substance over and above 

 w^hat the microscope has been able to provide, but no one has succeeded in 

 isolating any vital unit in this way, and up till now the cell, with all its 

 complications, remains the smallest form under which the living substance 

 has been found to exist by itself and independently of other living entities. 

 Of undoubtedly greater value have been those facts in regard to the composi- 

 tion of the cell that have been contributed by modern chemical research, 

 which will be discussed later. 



While, then, the fundamental substance of the cell has remained in its 

 innermost essence undiscovered, careful and extensive studies have been de- 

 voted to the mass of cell products of which the bodily tissues are built up. 

 Of the pioneer research-work in this field may be mentioned the investi- 

 gations of the elder Heidenhain into the glandular secretion in man and the 

 higher animals, as a result of which light has been thrown for the first time 

 especially upon the microscopical structure of the salivary glands and the 

 relation between the composition of their cells and the nature of their se- 

 cretion. In his footsteps followed Flemming, Altmann, the younger Heiden- 

 hain, and many other cytologists, who observed and compared the different 

 phenomena in the epithelial cells, both the secreting and the resorbing, in 

 the various organs of the body and the cells covering the surface of the body. 

 In this sphere the study of the origin and development of the granular forma- 

 tions has been most intensive. 



Nerve investigations 

 One field of inquiry that has especially occupied the attention of modern 

 cytology is the nervous system. Its highly complicated structure long re- 

 sisted all attempts at an explanation, until methods were discovered whereby 

 it is possible to colour only certain special elements, which can thus be ex- 

 amined in their entire length. These "elective" methods include impreg- 

 nation with metallic salts, which has been applied in various forms by the 

 Italian Camillo Golgi (1844-19x6), professor at Pavia, the Spaniard San- 

 tiago Ramon y Cajal, born in 1851, professor at Madrid and an unusally 

 thorough expert in the elements of the nervous system throughout the ani- 

 mal kingdom, the author of a number of papers on the subject, as well as 



