540 THE HISTORY OF BIOLOGY 



the monumental work Histologic du sysfeme nerveux, and the Hungarian Stefan 

 Apathy (1863-1913), professor at Koloszvar. Another method that was pro- 

 ductive in this respect has been the incravital methylene blue-dyeing method, 

 which was discovered by Paul Ehrlich (1851-1915), disciple of Koch and 

 principal of the laboratory of hygiene at Frankfurt am Main, and which 

 has been further applied especially by A. Bethe, professor at Strassburg. 

 Others who have studied the nervous system include the aged Kolliker, the 

 Frenchman Louis Antoine Ranvier (1835-1911), professor at Paris and 

 active worker in many branches of cytology, and also Gustaf Retzius (1841- 

 1919), son of the above-mentioned anthropologist and early in life an assid- 

 uous worker in this sphere. Neurological research has to a certain extent 

 sought to ascertain the structure of the actual nerve-cells and their internal 

 modifications during different stages of activity; as expressions for the phys- 

 iological condition in the protoplasm of these cells have been characterized 

 the granular formations amassed in stages of rest and disappearing upon 

 irritation, which are called tigroid substance, owing to their appearance, 

 or "Nissl's granules" after their discoverer, Friedrich Nissl, hospital doc- 

 tor at Frankfurt am Main (died 1919). Still greater interest, however, has 

 been devoted to the problem of the connexion between the nerve elements, 

 which indeed is of vast importance also from the physiological point of 

 view. In this field there have been two mutually opposed theories. Even 

 His had observed that there grow out from the embryonic nerve-cells threads, 

 which become longer and longer. Later on, Kolliker, Cajal, and Retzius, 

 among others, held the view that these threads give rise to the nervous 

 fibrillar and that the nervous system is thus formed of a number of mutually 

 independent elements, consisting of a cell with its concomitant nerve-thread 

 and connected with its neighbours only by contact. In opposition to this 

 view. Apathy in particular has maintained that the nerve-thread is formed 

 of a whole series of cells and that its ramifications extend not only up to, 

 but also into, the plasm in the ganglion-cells. The conflict between these 

 two lines of thought was at one time quite lively, but apparently died down 

 without either party's being able to claim a decisive victory. 



Muscle investigations 

 Besides the nervous system, the musculature early attracted the attention 

 of the cytologists, especially the cross-striated musculature, the complex 

 structure of which had long withstood all attempts to interpret it. William 

 Bowman (1816-91), professor of physiology in London, was the first to 

 make any weighty contribution towards the solution of the problem. In a 

 treatise printed in 1840 he describes how the muscle is composed of fibrillar, 

 surrounded by a substance that he calls sarcolemma, and how the fibrillar 

 are divided crosswise into laminx of various degrees of density. During the 

 time that has elapsed since then, muscular histology has had many students. 



