402 The Study of Zodlogy in Germany. (July, 
affecting the brain that the ganglion cells may be quite easily 
isolated. To effect this a very small piece of the brain — calf’s 
brain is perhaps the best — is placed in fifty or sixty times its 
volume of the solution for twenty-four hours, and then carefully 
teased out under a good dissecting microscope. 
Both weak chromic acid and alcohol may be used for isolating 
muscular fibres. Flies and beetles are perhaps the best for this 
purpose. The muscles of the wings (not those of the legs) 
should be torn out with fine forceps, and little bits, the smaller 
the better, placed in thirty per cent. spirit for twenty-four hours, 
and then dissociated or pulled apart on a glass slide, with fine 
needles. With sufficient care it is possible to separate the single 
fibrillæ of each fibre, and when stained with hamatoxiline the 
7 ; T alternating lines, dark and light (Fig- 
a as ure 75), appear very sharply. These © 
(Fra. 75.) ISOLATED MUSCULAR lines are those that make the muscles 
BEETLE, ” transversely striated. The cause of this 
striated appearance is not yet fully determined, but it is appar- 
ently connected with greater perfection of the muscular fibre 
than is found in the unstriated form. Different as is muscle in 
appearance from cells yet it originates from them, and is in fact 
formed of metamorphosed cells, by a series of changes all as great 
as those which produce bone. 
We have still to notice a very important class of procedures, 
namely, injections. In the higher animals we find two dis- — 
tinct sets of vessels ramifying through the whole body: one of 
these is the system of blood-vessels, the other the lymphatic sys- 
tem. As is well known to all, the blood-vessels branch out into 
very fine tubes that form a complicated net-work in every 
part of the body, so fine that it can only be followed when the 
tubes or capillaries have been artificially filled with a colored | 
matter. The same is true of the lymph-vessels, but to an even 
greater extent. Many of the structures of the body are per- 
meated by connective tissue, and in this tissue there are DW 
merous cavities filled with fluid; they are in communication 
with very delicate tubes, the lymphatic capillaries, which soon 
unite into larger canals, and these form branches which grad- 
ually join together and lead to the thoracic duct or main stem, 
which empties into the veins just before they open into the . 
heart. The branches of this tubular system are provided with 
valves so arranged that the liquid contained in the tubes can 
only pass upward or towards the main stem. Now when any 
