84 CHAPTER VI. 



SQUIRE, in his Methods and Formulas, etc., p. 81, says that 

 origanum oil (meaning the commercial product) is nothing 

 but oil of white thyme more or less adulterated (see next ), 

 and that the product sold as 01. Origani Cretici is probably 

 oil of marjoram. 



114. Oil of Thyme. FISH (Proc. Amer. Mic. Soc., 1893 ; 

 Zeit. f. wiss. Mik., xi, 4, p. 503), following BUMPUS, says that 

 for most of the purposes for which origanum oil has been 

 recommended, oil of thyme will do just as well if not better. 

 After one distillation of the crude oil of thyme it is of a red- 

 dish-brown colour, and is called the red oil of thyme ; when 

 again distilled it becomes colourless, and is distinguished as 

 the white oil. The red oil is just as efficient as the white for 

 clearing. 



Schimnieland Co., in their Report of October, 1895, p. 69, 

 state that in France white oil of thyme is adulterated with 

 oil of turpentine to the extent of as much as 50 per cent. 



115. Sandal-wood Oil (NEELSEN and SCHIEFFERDECKER, ibid.). 

 Very useful ; but its high price is prohibitive. 



116. Oil of Cajeput. This oil is, I believe, frequently used as a clearer 

 by the botanists. I have used it myself and found it to clear well, but to 

 be rather thin. CAKNOY AND LEBRTJN (La Cellule, xiii, 1, 1897, p. 71) 

 have found it useful for clearing celloidin sections. It dissolves celloidin 

 very slowly and clears without shrinkage. 



117. Oil of Turpentine. Generally used for treating sections that 

 have been cut in paraffin, as it has the property of dissolving out the 

 paraffin and clearing the sections at the same time ; but many other re- 

 agents (see 139) are preferable for this purpose. If used for alcohol 

 objects it causes considerable shrinkage, and alters the structure of cells 

 more than any other clearing agent known to nie. Turpentine has, I 

 believe, the lowest index of . refraction of all the usual clearing agents 

 except bergarnot oil ; it clears objects less than balsam. 



118. Carbolic Acid. Best used in concentrated solution in 

 alcohol. Clears instantaneously, even very watery prepara- 

 tions. This is a very good medium, but it is better avoided 

 for preparations of soft parts which it is intended to mount 

 in balsam, as they generally shrink by exosmosis when placed 



