188 PHYSIOLOGY CHAP. 



the diffuse nervous network of Gerlach and Golgi, inasmuch as 

 it is continuous with the fibrils that enter from the periphery, 

 and those which leave in the axis of the single process of the 

 nerve-cells of Hirudo. The filaments of this network are therefore 

 in direct continuity with the sensory or motor fibrils that enter and 

 leave the ganglion cells, and which form the intracellular fibrillary 

 network referred to above. All the ganglion cells are thus directly 

 connected among themselves by the continuity of the fibrils, which, 

 according to Apathy, are the essential* elements of nerve con- 

 ductivity. At the periphery of the system again, both in the 

 epithelial cells and in the sensory cells and muscles, the fibres 

 never exhibit free endings but anastomose among themselves to 

 form a network, in the same way as the arteries and veins form a 

 single continuous system by means of the capillary network. 



Bethe confirmed Apathy's results in the most essential points, 

 for vertebrates as well as for invertebrates, by another method, viz. 

 elective staining of the fibrils. He finds that very different re- 

 lations prevail in different classes of animals between the ganglion 

 cells and the fibrils. In Arthropoda the extracellular fibrillary 

 network is well developed, while comparatively few h'brils enter or 

 leave the ganglion cells to form an intracellular network. In 

 vertebrates, on the other hand, most of the fibrils pass through the 

 cell, without forming a network within it ; on the contrary an 

 extracellular network is formed by the anastomosing of the fibrils 

 that surround the cell. 



This last statement of Bethe's is contradicted, as we have seen, 

 by the most recent work of Golgi, Donaggio, and Semi Meyer, 

 which shows that the methods employed by Bethe bring out 

 only the coarser fibrils, leaving the more delicate intra- and peri- 

 cellular fibrils unstained. Bethe, on the strength of his own 

 observations, and of an experimental argument which we shall 

 examine below, reduces the importance of the ganglion cells, and 

 holds them to be mere stations for the passage and reinforcement 

 of the nerve current, while the central activity of the system is 

 developed outside the cell in the intercellular elementary network 

 of the grey matter ; Donaggio, on the contrary, holds that the 

 cell probably represents the true centre for the reception of the 

 excitatory impulse and for its synthesis and transformation. 



As regards the theory of the unitary structure of the nervous 

 system of vertebrates, Held supports Bethe in essentials, on the 

 strength of his own observations ; Golgi, Veratti, Donaggio main- 

 tain an absolute reserve ; Semi Meyer and Lugaro, while they 

 admit the importance of Bethe's observations, deny that these prove 

 the applicability to vertebrates of Apathy's results for inverte- 

 brates, so as to overthrow the neurone theory, according to which 

 the relation of the separate elements of the system is merely one 

 of contact. Lugaro admits as a possibility, in regard to the question 



