and Laboratory Methods. 



1321 



fluid carbon-dioxide may be obtained in tanks, and its power of rapid freezing, 

 have caused it to be preferred to ether and similar fluids. In every active patho- 

 logical laboratory the freezing microtome is in daily use. Perhaps its greatest value 

 lies in the fact that thin sections may be made within a few minutes after the 

 removal of tissue from the body, and in a few minutes more these sections may 

 be hardened, stained, cleared, and mounted. The surgeon may thus be given a 

 positive diagnosis of the microscopic condition of diseased tissues while he 

 proceeds with an operation. 



The carbon-dioxide microtomes commonly used have, however, several draw- 

 backs which have served to render them far less useful than they should be. 

 From the practical standpoint their most serious drawbacks are a tendency to 





Fig. I. 



A. Cover of freezing stage ; B. Glass track for carrying knife ; E. Spiral spring ; 



F. Tubal base of knife-stage ; I. Wheel : J. Nut for attaching axial 



tube to tank; M. Handle of tank-valve; N. Pointer. 



become clogged and a great wastefulness of gas. From the scientific standpoint, 

 lack of control over the temperature of the freezing stage serves to give rise to 

 an " over-freezing," which produces marked alterations in the tissues. In order 

 to remedy these defects the machine described below was devised. In designing 

 a practical machine I had the able assistance of Mr. E. F. Northrup. The 

 Bausch & Lomb Company, who have undertaken its manufacture, have also 

 offered suggestions that have proved of much value. 



Figure 1 shows the machine as it stands ready for use. It is supported 

 directly by the nozzle of the carbon-dioxide tank. This offers a firm and con- 

 venient means of attachment, but, if desired, a heavy tubing may be utilized to 



