3 -54 The American Naturalist [Apri i, 



room is divided into two apartments connected with double doors, 

 one of which is provided with hot water pipes. 



"With these arrangements it was easy to keep the temperature 

 within one or two degrees, above or below, that of the outer air, what- 

 ever the weather might be. The interior is furnished with tables in 

 benches, work-tables, etc., for breeding-cage and root-cage work, and 

 contains a brick-lined trench, three feet wide and fifteen feet long by 

 three feet deep, cemented within, and filled with earth, for the larger 

 plants, and for small plot experiments." 



MICROSCOPY. 1 



Notes on Celloidin Technique.— The high value of celloidin 

 as an imbedding mass is well-known, and its superiority over all meth- 

 ods requiring heat is unquestioned, yet, from the fact that its manipu- 

 lation has been attended by many difficulties, it has not come into 

 general use. During the past two years I have tried the methods rec- 

 ommended by various authors and have found none entirely satisfac- 

 tory, especially where very long series were necessary. The results of 

 my experience are embodied in the following method : 



The prepared plates or fragments are placed in an air-tight cham- 

 ber; a four-ounce salt-mouth bottle being very suitable for this pur- 

 pose. Pour into this bottle just enough ether-alcohol (equal parts 

 acid-free sulphuric ether and absolute alcohol) to cover the fragments. 

 The ether-alcohol should be added until after occasional shaking no 

 celloidin remains undissolved ; this may take several days. It should 

 finally possess the consistency of a very thick oil. The solution thus 

 obtained may be labelled No. 4. No. 3 is obtained by taking two vol- 

 umes of No. 4 and diluting with one volume of ether-alcohol. No. 2 

 by proceeding in a like manner with No. 3. No. 1 is a mixture of 

 absolute alcohol and sulphuric e th< r in equal parts. 



The saturation and final imbedding is accomplished thus: The 

 object is transferred from 95% alcohol to solutions 1, 2, 3, 4 success- 

 ively, in each of which it remains from a tew hours to days, depend 

 ing opon the size and permeability. For pieces of tissue 2 mm. in 

 diameter twenty -four hours in each will generally suffice. For a large 

 brain, e. g. that of a cat, a week in each will not be too long. 



In imbedding, unless orientation is desired, the ordinary paper box 

 is best. A thin plate of lead is placed in the bottom and the imbed- 



