444 A. B. MAOALLUM. 



as with it one is apt to get beautiful preparations of the liver in 

 which the gall-capillaries, gall-ducts, blood-capillaries, the 

 nerves, and the elements of the hepatic cells and their nuclei 

 are demonstrated in a way that I have found equalled by no 

 other method of manipulation. The value of chromic acid and 

 gold chloride in this respect I shall refer to again in a subse- 

 quent paper. 



Sections of the liver ofNecturus are not of any value when 

 they are of less than 0'020 ra. in thickness, that being less than 

 half the average diameter of the hepatic cell. 



In the case of the human liver chromic acid was the only 

 reagent used in hardening. The sections were made with the 

 paraffin method, and were subsequently treated in the manner 

 already outlined. I found that uniformly thick or uniformly 

 thin sections did not answer well, for in these either but short 

 pieces of nerve-fibres or fibrils could be seen, or else they were 

 obscured by the thickness of the section. I managed to obtain 

 sections about half an inch square, which had a thickness at 

 one edge two to three times greater than at the opposite one, 

 so that the thickness decreased gradually from one edge to the 

 other. With these sections I was able to see and follow a fibre 

 in its full extent, together with its divisions or branchlets, and 

 thereby gained all the advantages of a thick and a thin section, 

 with the faults of neither so far as tracing the nerves is con- 

 cerned. 



The success of the preparations of the human liver was the 

 exception and not the rule. About 10 per cent, or at most 

 20 per cent, of them only were valuable for all the purposes for 

 which I made them. Sections from the same piece of liver, 

 when treated under exactly like conditions but in different 

 dishes, proved to be not equally successful, some being indif- 

 ferent or worthless. Why this is I do not know. In the case 

 of a very strong colouring with the gold so much as to obscure 

 the structure, I used a ^ per cent, solution of potassic cyanide 

 as recommended by Cybulsky.^ By putting the over-stained 

 ^ion in this solution the proper depth of colour is obtained 

 1 'Zeit. fur wiss. Zoo!.,' Bd. 39, S. 657. 



