H 



SCIENCE-GOSSIP. 



PHYSICAL AND MECHANICAL DISINFECTION. 



A MEETING of the members of the Civil and 

 Mechanical Engineers' Society was held on 

 April 22nd, in the Westminster Palace Hotel, 

 when a paper on "Physical and Mechanical 

 Disinfection " was read by Mr. W. Noble 

 Twelvetrees. This subject, interesting alike to 

 civil engineers and others concerned in municipal 

 affairs, was dealt with in a comprehensive manner 

 and illustrated by a number of interesting diagrams 

 showing the various forms of apparatus used in 

 laboratory practice and in public institutions. 



Favoured inhabitants of the world in the present 

 year of grace are perhaps occasionally apt to overlook 

 the useful work done in past generations, and 

 those who imagine that efficient hygienic regulations 

 originated during the present epoch are reminded 

 by Mr. Twelvetrees that, in the earliest ages, 

 disinfection and sanitary precautions received due 

 attention. Amongst the earliest evidences of this 

 fact, are mentioned the laws of Moses and of 

 Lycurgus, and of heathen religious practices, all 

 showing an intelligent recognition of the value 

 of disinfection. Having called attention to the 

 practical good sense the ancient Romans evidenced 

 by their attention to drainage, ventilation and 

 water-supply, and by the appointment of State 

 physicians in their cities and towns, the writer 

 pointed out that in the middle ages the civilized 

 world suffered a relapse, diseases and epidemics 

 being regarded as " dispensations of Providence, 

 which it would be sinful to combat, save by 

 prayer and penance." The growth of a revived 

 interest in sanitary science was next traced, also 

 the recent development of the germ theory, which, 

 aided by the practical science of bacteriology, has 

 rendered the most invaluable assistance to those 

 responsible for promoting the health and well- 

 being of the community. 



Speaking of bacteria, or micro-organisms, which 

 have been proved by eminent men of science to be 

 at the root of all diseases, and injurious changes in 

 organic substances, Mr. Twelvetrees remarked, 

 "It is probably not exaggerating matters to say, 

 that the self-respecting citizen has no better opinion 

 of a microbe than an ordinary police magistrate 

 has of a cyclist." He pointed out, however, that 

 the large majority of these omnipresent organisms 

 performed useful work by resolving organic 

 substances into their constituent elements. The 

 physical forms and characteristics of micro- 

 organisms were next dealt with as affording an 

 indication of the means to be adopted for extir- 

 pating or reducing the numbers of harmful species, 



Mr. Twelvetrees next described and illustrated 

 the various forms of collecting, cultivating and 



sterilizing apparatus in laboratory use, then 

 proceeded to discuss the question of disinfection by 

 physical means. The drawbacks attached to the 

 use of hot air appear to be the high temperature 

 required and the length of time necessary for 

 sterilization. Steam is recommended as the most 

 efficient and convenient agent, but an important 

 distinction is drawn between the relative values of 

 superheated and saturated steam, the former, at 

 a temperature of 285 F., being no more efficient 

 than hot air, whereas the latter, even at 214 F., 

 is extremely rapid in effecting sterilization. Satu- 

 rated steam may be applied in modern apparatus, 

 either under varying pressures or in the form of a 

 continuous current, at atmospheric pressure. The 

 leading types of English, Continental and American 

 apparatus were fully described and illustrated, the 

 results of experiments by leading authorities 

 being quoted in detail. Among English forms of 

 apparatus one including a novel and ingenious 

 feature is that invented by Dr. Thresh, Medical 

 Officer of Health for the County of Essex. The 

 "Thresh" Disinfector, used on the "current 

 steam " system, utilises the well-known physical 

 fact that water containing substances in solution 

 possesses a boiling point proportional to the 

 specific gravity of the liquid. By using a solution 

 of calcium chloride (specific gravity, i'36) a 

 temperature of 225° F. is attained, steam being 

 given off at about 220 F., thus ensuring absolute 

 sterilizing efficiency. The apparatus is very simple 

 in construction, and being open to atmospheric 

 pressure there can be no risk of explosion. 



Mr. Twelvetrees next illustrated the most im- 

 portant points to be observed in the construction 

 of public disinfecting stations, and passed on to the 

 consideration of incineration as a means of destroy- 

 ing infectious matter which is not of sufficient 

 value or is otherwise unsuitable for treatment in 

 an ordinary apparatus. Chemical disinfection, 

 according to authorities quoted, though not with- 

 out its uses, is not to be regarded as a satisfactory- 

 means of sterilization. Mechanical disinfection, 

 including natural and artifical filtration, was 

 discussed somewhat fully, as being of the greatest 

 public importance. Sand filtration has been found 

 by Dr. Frankland to remove 98-4 per cent, of the 

 organisms from Thames water. The assistance 

 rendered to filtration by settling reservoirs, in 

 which the water is purified by deposition, by 

 oxidization, and by the destruction of harmful 

 germs by inoffensive species was instanced, as 

 also the valuable results obtained by the use on 

 a large scale of the Porter-Clark and other systems 

 of water-softening apparatus. 



