158 Transactions of the Society. 



allowing the blood to flow out from the wound made to expose it. 

 If the injection is successful, organs and tissues becomie very 

 quickly ready for the second stage of the method, and one must 

 rapidly proceed to their extraction and reduction into small pieces, 

 which are left in the fixing fluid for a short period, corresponding 

 to about one-third or one-half of the time needed for the fixation 

 of non-injected material. Should it be particularly interesting to 

 have the outermost layers of certain organs well stained, these 

 must be fixed with some of the surrounding tissue, such as fatty 

 or connective tissue, the pia mater in the caseof the central nervous 

 system, etc. I have at present little experience of the fixation of 

 material from low vertebrates and invertebrates. In general I 

 should advise proceeding by tentative experiments, which are also 

 necessary for the systematic study of the internal apparatus in 

 some determined tissues, as the moment in which they become 

 ready for the subsequent treatment appears to vary a little in 

 almost every one of them. The fixation at a temperature vary- 

 ing between 25 and 37° C. has been attempted with some success, 

 particularly in the case of cortex cerebelli of mammalia. It 

 leads, however, to some special results which M'ill be dealt with 

 afterwards. 



2. Impregnation. 



The pieces are quickly washed twice in distilled w^ater, their 

 surfaces made smooth if necessary, and then placed in a 1*5 p.c. 

 solution of AgNOs. For very small fragments and structures 

 which are easily impregnated, as the Fallopian tube of small 

 mammals, 1 p.c. AgNOg can be used. For pieces of spinal cord 

 of adult animals and organs containing much fat, the strength of 

 the AgN0:5 solution may be raised to 2 p.c. The quantity of 

 AgNO.} solution changes according • to the number of pieces ; 

 generally, no more than five or six are put in a specimen bottle 

 of an approximate capacity of 30 c.c. They are left in the silver 

 bath from twenty-four to forty-eight hours, according to their size. 

 A longer stay, though often without danger, should be avoided as 

 precipitates may form. As a rule the pieces, once in the AgNOj 

 solution, are kept away from the light and at room temperature. 

 In winter and if the temperature of the laboratory fails very 

 much during the night, one may have recourse to an incubator at 

 25-28° C. The use of an incubator at 36-37° C. may be attempted 

 with success for the spinal cord of adult mammals, and for pieces 

 which are difficult to impregnate. This practice may be attended 

 by good as well as by negative residts, and ought to be arrived at 

 by tentative experiments, in order to establish the most suitable 

 length of time during which the pieces may be safely left in the 

 "incubator at certain temperatures. 



