Meek, Choroid Plexus. 299 



tion under the influence of the ether, and an accumulation of the 

 fluid. A flow of about two drops per minute develops. If i per 

 cent pilocarpin now be injected through the femoral vein the 

 secretion becomes more marked, and may more than double in 

 amount. An injection of atropin will abolish the secretion 

 entirely. 



It is realized that the account just given does not contain suf- 

 ficient data. Many experiments should be made before definite 

 statements are submitted, regarding the rate or amount of flow, 

 or the time in which it develops. It is hoped that these omissions 

 may be supplied in some succeeding paper. The important fact, 

 however, seems perfectly clear, and that is, that the secretion of 

 the cerebro-spinal fluid is accelerated by pilocarpin and retarded 

 or abolished by atropin. 



Microscopic examination has been made of the plexuses of dogs 

 and rabbits that had been under the influence of ether for 20 min- 

 utes, and also of rabbits, guinea pigs, and 



rats injected with muscarin. The latter ^^^^ ^^ /'•^'^^J.'S '^ 

 drug was most useful when diluted to l'-^^ /■:^''^''V\/if_/^'i:\ 

 1-500. Two injections were made from (^^lKi^i-:-'^^3i 

 15-20 minutes apart, and 15 minutes ;^^^^^^||i^^ 

 later the animal was killed, and the plex- -^^--f.wit--- - 



uses removed. The injections were F'g- 8. Three cells from an 



made with a hypodermic syringe, and adult rabbit's plexus after injec- 



I . . tion of muscarin. Magnification 



no anaesthetic was given. ^ at 1 u- 1, 



o . . X 1500. a, Margmal zone wJiicri 



In the rat, muscarin did not give de- has become a thin granular line; 6, 



cisive results, but in the case of rabbits clear spaces toward the apex; c, 



and guinea pigs the results were defin- basal granular zone. 

 ite. Often as many as two-thirds of the 



cells showed evidences of secretion. Fig. 8 shows cells from a 

 rabbit's plexus after treatment with muscarin. Normally, the 

 epithelial cells in the rabbit are about 6 micra high (see Fig. 

 4) but here the height has increased to 12 micra. A diflPeren- 

 tiation into two zones, a basal granular, and an outer clear, is 

 suggested, but it is not quite so well marked as in the fig- 

 ures of Pettit and Girard. The granulations, however, are 

 always heavier and more compact toward the base of the cell. 

 Clear spaces begin to appear toward the top, and rarely does the 

 stainable cytoplasm extend to the upper cell wall. Masses of 

 larger granules are common in the upper part of the cell where 





