Smallwood and Rogers, Moll us can Nerve Cells. 53 



the nourishment of the cell. Nelis claims that as the nerve cells change there is 

 a decrease of the tigroid substance which is accompanied with an increase in the 

 amount of the transparent bands. Holmgren believes that the localization of the 

 tigroid substance should coincide with the appearance of the canals, that the canalicu- 

 lar zone of the cell should be the tigroid layer free of ectoplasm. The tigroid 

 substance stands in a causal relation to the lymph clefts and is associated with their 

 activities. Where the clefts are especially dilated, a rich accumulation of tigroid 

 substance takes place. In more protracted periods of activity the clefts become 

 smaller and the tigroid substance vanishes; but in such places where the tigroid 

 substance remains, the clefts remain dilated. Electric stimulation points to the 

 same conclusion. The nerve cells, as a result of such a stimulus, receive new 

 supplies of tigroid substance and at the same time become somewhat larger; 

 accompanying this, there is a dilation of the lymph clefts. This leads one to 

 believe that the electric current calls forth an alteration of the circulatory relations. 

 Holmgren cites a number of investigators whose work bears directly on the inter- 

 pretation of these structures as follows: 



Adamkiewicz ('86) from his researches with injections could have made the 

 same report, that the nerve cells are furnished with their own blood vessels and 

 that the nuclei of these cells should present venous spaces, but these discoveries 

 have nothing to do with the sap canals which do not carry blood. From the work 

 of other investigators it is evident that blood vessels very rarely enter nerve cells. 



Fritsch ('86) found that blood vessels were constantly to be found in the giant 

 ganglion cells of Lophius piscatorius. Holmgren uses the results of Fritsch to 

 confirm his own belief that lymph spaces exist in the cell, but makes the additional 

 statement that the blood capillaries are supposed to be drawn into the cell through 

 endocellular branching processes. In 1900 Holmgren came to the conclusion 

 that these spaces in the cells were not to be considered as blood vessels but rather 

 as lymph spaces in so much as they do not carry corpuscles. Studnicka in the 

 same year expressed the same belief, though more indirectly. 



Nelis ('99) describes in nerve cells homogeneous non-staining bands of a skein- 

 like appearance found within the cell. These appear in various places in the cell 

 body. They exhibit various forms, half moon, spiral, corkscrew, and hang 

 together at the ends, but do not form a true reticulum. They are to be found in 

 the cells of the spinal and sympathetic systems as well as in the brain. They are 

 particularly prominent in animals which have been poisoned. Holmgren claims 

 that these structures are the same as are called "Saftkanalchen." 



Studnicka ('99) held that the canals are formed from the running together of 

 vacuoles which had formed in the cell in a row. 



Bethe ('00) opposes this view on account of the fact that he had observed 

 single canals which passed completely through several nerve cells and their cap- 

 sules at the same time. 



Fragnito ('00) regarded the canals as the remains of the interstices between 

 the neuroblasts, through whose melting together the single nerve cells are supposed 

 to come into existence. 



Pugnat ('97) believes that the canals force their way into the nerve cells from 

 without, as lymph capillaries. 



Pewsner-Neufeld {'02) studied the finer anatomy of the nerve cells in the 

 nervous system of the white rat and guinea pig. He does not find that there are 



