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GEOFFREY SMFrH. 
tions and of glycogen ; secondly, bj quantitative cliemical’ 
methods for the estimation of the proportions of fat and 
glycogen present in the livers of normal and of infected crabs. 
The histological work was done in conjunction with Mr. J. J. 
Conybeare, B.A., New College, Oxford, in Dr. Scott’s labora- 
tory, and we are indebted to Dr. Scott for much help. In the 
quantitative chemical estimations of fat and glycogen. Dr. 
Ramsden has given me much invaluable advice, and some of 
the earlier expeidments were done in his laboratory. The 
rest of the work was carried on at the Marine Biological 
Laboratory at Plymouth, and I am indebted to the Director 
and staff for their constant attention to my needs. 
At the end will be found a summary of the physiological 
action of Sacculina on its host. 
1. Micro-chemical Methods. 
Besides ordinary fat stains, e.g. scarlet R. and Sudan 3, 
two principal micro-chemical methods have been used for 
detecting and distinguishing fat — the Nile bine sulphate 
method and Weigert’s method. These two methods are not 
only useful for detecting fat, but they also throw light on the 
nature of the fat or lipoid concerned, as has been shown by 
Professor J. Lorrain-Smith and W. Mair Fats and Lipoids 
in Relation to Methods of Staining,” ‘ Skandinavischen 
Archiv fur Physiologie,’ Bd. xxv, 1912. See this paper for 
details of method and reference to literature). 
In the Nile blue sulphate method, sections of the tissue 
(preserved in formalin 6 per cent.) are cut on the freezing 
microtome and stained overnight in a saturated watery solu- 
tion of the stain. These are differentiated in 2 per cent, acetic 
acid, washed in water and mounted in gum. By this method 
neutral fat is stained red, fatty acid blue, while a mixture of 
neutral fat and fatty acid is stained purple of various degrees 
according to the amount of the two constituents present. The 
rationale of this stain, as explained by Lorrain-Smith and 
Mair, is ^Mhat in the watery solution of the stain there is a 
