148 Experimental Treatment of Trypanosonuiasis. 
We considered that treatment by injection into the cerebro-spinal space 
was impracticable in horses owing to the distance of the spinal canal from 
the surface, and to the fact that the spinal cord extends much further down 
the canal than in man. 
Lxperements with Silver Salts. 
Three Surra rats were treated with protargol in doses varying from 
0°5 c.c. of a 1-per-cent. solution to 1 cc. of a 2-per-cent. solution. 
Three Surra rats were treated with argyrol in similar doses. 
Three Surra rats were treated with silver nitrate in doses varying from 
1 c.c. of a 0°02-per-cent. solution to 1 c.c. of a 1-per-cent. solution. 
All these rats died at the usual time: death was not delayed, nor were the 
trypanosomes reduced in number in the blood. Post-mortem examination 
showed that they had died with the usual signs of acute trypanosomiasis, 
with very large spleens, etc. At the sites of injection of protargol there 
was cedema and brown staining of the tissues in a circumscribed area: there 
was more marked cedema and swelling after injection of argyrol, and edema 
and localised necrosis of the tissues after injection of silver nitrate. It 
would appear that the silver salts are not absorbed from the site of injection. 
Presumably they have a primary cauterising action on the tissues, and are 
quickly transformed into silver chloride, which is inert. 
' In vitro experiments were carried out with these three compounds, all of 
which are soluble in distilled water. Equal sized drops of blood containing 
trypanosomes and of the solutions were mixed, and the results observed 
under the microscope. 
Protargol solutions from 1/200 to 1/10000 produced very little effect ; 
in 1/200 dead trypanosomes were seen in 30 minutes, but many were alive 
in 24 hours. Silver nitrate in solutions from 1/200 to 1/10000 has much 
the same effect as protargol. | 
Some trypanosomes are killed in 30 minutes by the stronger solutions, 
but the remainder are as active as the controls up to 24 hours and longer. 
Argyrol (which contains 30 per cent. silver) in solutions of 1/1000 to 
1/10000. The stronger solutions are still less active than those of protargol 
and silver nitrate ; and the more dilute have no effect up to three hours. 
Thus it appears that these bodies have no effect except the early effects of 
the stronger solutions; they probably combine with the salts in the blood- 
plasma and corpuscles, and become inert. } 
Citrate of silver in its strongest solution of 1/4000 is also inert. 
