208 NIKOLAS KLEINENBERG. 



pezoides, whose embryos may be readily extracted from the 

 albumen without injury. 



A great part of the earliest formations of the egg can be 

 made out in the living state, the protoplasm being sufficiently 

 transparent to allow the internal parts to be seen ; but after- 

 wards the precise outlines of the cells disappear, and nothing 

 can be seen but the grosser structure. To make out the more 

 delicate structure it is necessary to employ reagents. 



Of tliese I have employed several : osmic acid applied in 

 the state of vapour gives good results ; but the preparations 

 obtained by the use of a mixture of picric with sulphuric 

 acid were more satisfactory. This reagent, however, has the 

 same drawback as osmic acid, namely, that of occasionally 

 producing swellings in the primitive blastomeres, a circum- 

 stance which, if it only slightly alters the normal conditions, 

 renders the preparations less sightly. This difficulty is over- 

 come by the addition of a little kreosote. 



As I am now able, after many experiments, to recommend 

 strongly the method of preservation which I have here used, 

 and for the majority of other animal tissues, especially for 

 the more delicate and perishable, I think it may be useful to 

 give the exact receipt. 



Prepare a saturated solution of picric acid in distilled 

 water, and to a hundred volumes of this add two volumes of 

 concentrated sulphuric acid ; all the picric acid which is 

 precipitated must be removed by filtration. One volume of 

 the liquid obtained in this manner is to be diluted with three 

 volumes of water, and, finally, as much pure kreosote must 

 be added as will mix. 



The object to be preserved should remain in this liquid 

 for three, four, or more hours ; then it should be transferred, 

 in order to harden it and remove the acid, into 70 per cent, 

 alcohol, where it is to remain five or six hours. From this 

 it is to be removed into 90 per cent, alcohol, which is to be 

 changed until the yellow tint has either disappeared or 

 greatly diminished. Alcohol of 90 per cent, is better than 

 absolute for preserving the more delicate structures for a 

 long time uninjured, and for keeping the preparation at the 

 proper degree of hardness. 



For colouring I use crystallised hsematoxylin dissolved in 

 the following mixture : — Prepare a saturated solution of 

 calcium chloride in 70 per cent, alcohol, with the addition 

 of a little alum ; after having filtered, mix a volume of this 

 with from six to eight volumes of 70 per cent, alcohol. At 

 the time of using the liquid pour into it as many drops of a 

 concentrated solution of hsematoxylin in absolute alcohol as 



