10 THE AMERICAN MONTHLY [Jannarj, 



mences. The cover-glass is allowed to float on this with the sputum 

 downwards for from a quarter to a half an hour. It is then washed for 

 a few seconds in nitric acid, one part, distilled water, two parts, and 

 afterwards in distilled water alone. It may then be dried and mounted 

 in balsam. 



Chloride of gold is employed as a staining agent when it is desirable 

 to bring out the exceedingl};' fine ramifications of nerve tissues, but care 

 is required in its use to avoid overstaining. The solution should be 

 very dilute, about one part of the gold salt to two hundred of distilled 

 water. The section may be placed in this from a quarter to half an 

 hour, and then removed, freely washed with a large quantity of distilled 

 water, to which a sufficient quantity of acetic acid has been added, to 

 render the water perceptibly acid, and placed in the light, which, act- 

 ing on the gold, gradually darkens it to a pale violet color. If the gold 

 solution has been too strong, or the immersion too prolonged, the sec- 

 tion will become of such a dark purple as to be almost useless. 



Diluted solution of osmic acid is useful for staining fat cells, but great 

 cai-e must be taken by the student to avoid the fumes, which are very 

 injurious to the eyes and the mucous membranes of the nose and throat. 

 The fumes themselves are sufficient to stain many delicate preparations, 

 and even to kill small insects. 



The stain or reagent which may be employed to identify starch cells 

 is : Iodine, i gramme ; iodide of potassium, 3 grammes ; water, looc.c. 

 A small quantity of this placed upon starch will turn it at once to a purple 

 color, and proves its nature beyond doubt. 



It is sometimes necessary in preparing vegetable sections to bleach 

 them prior to their undergoing staining processes ; for this purpose they 

 may be placed in a solution of chlorinated soda. This removes all the 

 green coloring matter harmlessly, and renders them, after copious wash- 

 ing, ready to take any stain. 



Insect Anatomy .—The student may now have acquired that dexterity 

 and steadiness of hand which w^ill be required in the study of insect 

 anatomy. No great difficulty will obtrude itself, but a draft will be 

 made on his patience, for nothing can be accomplished without great 

 cai-e and an entire absence of hurry. It is more conducive to success 

 if some of the larger insects ai'e chosen to begin upon. The common 

 kitchen cockroach will be convenient and interesting to commence on. 

 Chloroform offers a safe and at the same time the least painful agent for 

 killing insects. The one to be dissected should be placed on a piece of 

 blotting-paper under a glass, with about thirty drops of chloroform. In 

 a minute's time it will have been killed without suffering. Before pro- 

 ceeding to the dissection form a definite plan, and select the particular 

 part to be investigated. The abdominal viscera present the least diffi- 

 culty. In this, as in all cases, first remove with scissors such embarrass- 

 ing organs as the legs, wings, and antennse ; the insect may then be se- 

 curely fastened below water, to which a few drops of alcohol has been 

 added, the alcohol slightlj^ hardening the delicate viscera, while the 

 water floats them, and keeps them from becoming entangled. There 

 are two methods by which this very necessary security may be attained ; 

 that most generally recommended is by pinning the insect to a layer of 

 entomological cork, attached to some sheet lead. A plan which has 

 been adopted with great success is as follows : Cut a piece of gutta- 



