STRUCTURE OF NEPHRIDIA OF THE MEDICINAL LEECH. 289 
iiephridia in order to ascertain the structure of the walls 
of the blood-vessels and of the ducts of the gland. An 
interesting structure in the substance of the gland-cells 
themselves was revealed by this method. 
5. Injection of the vascular system with soluble Berlin- 
blue was practised with some success so far as the injection of 
the finer vessels of the integument, &c., was concerned, but I 
have not succeeded in injecting the capillaries of the nephri- 
dium itself. I have been at present equally unsuccessful in 
injecting the ducts of the nephridium. The mode of injection 
made use of was that used by Moseley in his injections of in- 
sects, which consists in using a small glass tube drawn out 
to a capillary termination serving as the nozzle, a caoutchouc 
tube being attached to the other end of the glass tube. When 
the little apparatus is filled with injecting fluid it suffices to 
compress the caoutchouc tube in order to obtain sufficient 
pressure and sufficient flow of liquid for the injection of very 
minute organs. I also made with Professor Lankester some 
injections of indigo carmine into the body substance of an 
uninjured Leech by means of a subcutaneous syringe. The 
Leeches lived well after receiving a cubic centimetre of the 
indigo-carmine solution, but we have not as yet obtained 
any definite results as to the excretion of indigo by the 
nephridia or other organs. 
6. The most important method of which I availed myself 
in conjunction with the ^^study of whole nephridia, is that 
of section-cutting ; sections of nephridia wxre obtained either 
by cutting whole Leeches or by cutting only a single nephri- 
dium and its surrounding tissues isolated for the purpose. 
In either case the Leech was prepared by killing with 
chloroform, and w'as moderately stretched by means of a pin 
at each end fixing it in a gutta-percha trough. Chromic 
acid of -^th per cent, aqueous solution was then allowed to 
act on the Leech for eighteen to twenty-four hours. The 
specimen was next removed to half a pint of alcohol (60 per 
cent.), and removed to a second half pint on the following 
day. After three or four days in the second quantum of 
alcohol sections should be cut and stained. The staining 
is more successful in recently hardened specimens than in 
those which have been preserved many months. Chromic 
acid was preferred for the hardening process to Kleinen- 
berg^s picrin solution or to pure alcohol. 
The sections w'ere cut by the aid of a simple screw micro- 
tome, and from forty to sixty could be obtained and pre- 
served in their order of sequence in the region of a single 
pair of nephridia. 
