MODE OF SPREAD OF INFECTIVE DISEASES. 773 



should be round, or nearly round, in order to avoid the 

 presence of corners in which the disinfection may very 

 readily he imperfect. It must also he home in mind 

 that hot air containing a certain amount of steam does 

 not by any means have the same effect as a good 

 current of steam without any air (see p. 665) ; those 

 forms of apparatus are untrustworthy in which steam is 

 present even under high pressure, hut not in such 

 quantity that after filling the apparatus a good current of 

 steam escapes from it. It does not seem to be necessary 

 to raise the temperature of the steam by employing 

 saline solutions ; it has been definitely proved by 

 numerous experiments in Koch's laboratory, and by 

 comparative tests by Wolff which were made on a num- 

 ber of machines and in a trustworthy manner, that even 

 very large objects (balls composed of 22 woollen blankets) 

 are completely disinfected by exposure for one to two 

 hours to a current of steam at 100 C. One hour 

 suffices for smaller objects, and half an hour for linen 

 and clothing, the time being reckoned from the moment 

 when the steam which escapes shows a temperature of 

 100 C. 



By this plan the injury done to the materials is very 

 slight. Linen, feather beds, mattresses, clothing, 

 printed matter, &c., are quite unhurt, but sensitive 

 colours are somewhat altered. Disinfection by heat 

 cannot be employed for objects made of leather (boots), 

 gum, or caoutchouc, and bound books. 



No definite statement can be made as to the special 

 advantages of one or other of the disinfecting appara- 

 tuses mentioned above ; at all events, they are all trust- 

 worthy and useful. They are prepared in various sizes 

 and at various prices, and one ought to be in use in every 

 town. 



In Gottingen a very simple and cheap apparatus has heen Special 



introduced provisionally, and acts extremely well. It is con- f^jj^f* 1 f 

 structed on the same principles as the sterilising apparatus ratus for dis- 

 commonly used in laboratories and described on page 665, inf ection. 

 being merely correspondingly larger. It is desirable to have 

 two of these machines of different sizes, the one being 7 

 metres in height and 50 cm. in diameter, the other 1'4 metres 



