30 JOURNAL OF THE [January, 



After the animals have been paralyzed in the neutral hydrochlo- 

 rate solution they are immediately covered with the fixing medium 

 and thereby killed. 



The number of fixing reagents that may be used is of course 

 limited. For, hydroxylamine being a powerful reducing medium, 

 all easily reducible agents, such as osmic acid, corrosive sublimate, 

 chloride of gold, of platinum, etc., cannot be directly applied. 

 The hydroxylamine must first be worked out with water. Alco- 

 hol, acetic and picric acids, and mixtures of these two acids may 

 be directly applied, and with these a good histological slide may 

 always be obtained. 



The strength of the solution depends, of course, on the nature of 

 the animal to be mounted. In the case of a few special objects I 

 find the following directions may be respectively used : 



I. Stentor cceruleus. — Place the Stentors for ten or fifteen min- 

 utes in a 0.25-per-cent solution of the hydrochlorate. A large pro- 

 portion of the animals soon stretch themselves out and remain in 

 the semi-distended condition which free-swimming Stentors usually 

 show. No subsequent contraction occurs. The paralyzing effect 

 of the hydroxylamine is soon apparent, but is, however, not suf- 

 ficiently complete to commence the fixing process. The paralysis 

 must first extend to the cilia. After some ten minutes the cilia 

 of the peristome move irregularly and slower, and finally cease 

 moving altogether. This change must be carefully noted, for at 

 this step the Stentors are suddenly flooded with a concentrated solu- 

 tion of picric acid mixed with a 5-per-cent solution of acetic acid. 

 The majority of the Stentors are now pear-shaped; a few are dis- 

 tended their full length ; while others have the same round shape 

 that Stentors assume when fixed before having been previously 

 paralyzed. The peristome cilia of each individual remain ex- 

 tended and are not drawn back. Sometimes the smaller forms 

 are killed inside of ten minutes through the action of the hydrox- 

 ylamine, the protoplasm swells, and the animals are entirely de- 

 formed. It is consequently always necessary to observe the action 

 of the hydroxylamine from time to time through the microscope, 

 and to add the picric acid before the protoplasm in the larger forms 

 appears to swell; for if left too long the hydroxylamine will act as a 

 poison on the protoplasm, as has been shown by Loew in his experi- 

 ments with vegetable protoplasm. If the action be stopped, how- 



