January, 1910.] 



41 



Plant Sanitation. 



the bacteria ; several bacteria are known 

 to produce black colouring matters in 

 this way. These biscuits had beeu coagu- 

 lated with formalin. Iu another case, 

 the biscuits when held up to the light 

 were seen to be mottled with dark brown 

 pitches. These were dark biscuits 

 which had not been subjected to any 

 hot w T ater treatment. In many ex- 

 amples of dark coloured biscuits it will 

 be found that the colour is due, at least 

 in part, to a thin film of brown colouring 

 matter on the under (?) side of the bis- 

 cuit. In some cases, if the biscuit is 

 sliced into two horizontally, a marked 

 difference will be seen in the colour of 

 the two halves, the upper half being 

 more or less amber coloured, while the 

 lower half, though of the same thick- 

 ness, is dark, owing to the presence 

 of this brown film. The presence of 

 this film may be demonstrated more 

 clearly by cutting a thin slice through 

 the biscuit and placing it in chloroform 

 or some other solvent under the micros- 

 cope. As the rubber absorbs the solvent 

 and swells, the film on the exterior 

 shows up quite plainly. This film is 

 composed of some amorphous brown 

 substance whose nature has not been 

 ascertained, usually with some yeast 

 cells ; and, as a rule, it is spread uni- 

 formly over one side of the biscuit. 

 In the case of the mottled biscuits re- 

 ferred to above, the discolouration, 

 which was quite superficial, was due to 

 an abnor mal development of this film, 

 and most of it was collected in patches 

 instead of being spread uniformly over 

 the surface. Yeast cells were present 

 in abundance in the sediment obtained 

 on dissolving the rubber in chloroform 

 or carbon bisulphide. 



Bacteria and yeasts appear to be the 

 chief organisms concerned in this spot- 

 ting of rubber biscuits ; of course, moulds 

 grow on the surface, but I have not up 

 to the present observed any effect which 

 could be attributed to them. An exact 

 investigation into the causes of these 

 spots would occupy one or more investi- 

 gators for at least a year, and would 

 require all the appliances of modern 

 bacteriological research. It would de- 

 mand a strictly scientific examination, 

 in each individual case, of the fungus 

 and bacterial flora of the collecting 

 cups, the setting pans, the curing house 

 and the water supply, together with 

 experiments to determine which of the 

 organising found would grow in latex 

 or wet rubber, and their effect on either. 

 But although this problem cannot be 

 dealt with under the present circum- 

 stances, it is possible to lay down more 

 or less general empirical rules as to the 

 course to be adopted in order to get 



rid of the cause of these brown or 

 black spots. It is unlikely that the 

 effect is in any way connected with 

 the tree, and it must be assumed for 

 the present that some organism is 

 introduced into the latex or the coagu- 

 lated rubber either by the wind or by 

 the water supply. In either case, if the 

 collecting cups, pails, etc, are once infect- 

 ed, they will remain infected, and the 

 biscuits will continue to be discoloured, 

 until some method of sterilisation is 

 adopted. Therefore, when this trouble 

 makes its appearance, all collecting cups 

 should ho boiled, and the dishes, pails, 

 etc. scalded with boiling water. It has 

 been found sufficient to do this once, but 

 it would be a wise precaution to scald 

 the dishes and pails periodically, as 

 part of, the general routine of the 

 factory. Iu one instance, that of the 

 mottled biscuits referred to above, this 

 treatment was adopted ; and the super- 

 intendent writes : " With reference 

 to the black biscuits about which I 

 wrote to you some months back, it may 

 interest you to know that since I took 

 your advice and boiled all the utensils 

 used, and had my store thoroughly 

 cleansed, no black biscuits have put in 

 an appearance."* 



If the infection is introduced with the 

 water supply, the above treatment will 

 not stop it, because the dishes will be 

 reinfected. To determine whether the 

 water supply is at fault, biscuits should 

 be made, using water which has been 

 boiled and cooled, and these should be 

 compared with biscuits made with the 

 unboiled water. Of course, the dishes, 

 etc., must be sterilised before the experi- 

 ment is attempted, otherwise that pos- 

 sible source of infection will not be ex- 

 cluded. If the water were infected, and 

 no other source of supply were available, 

 more elaborate experiments would be 

 required to determine whether the in- 

 fection could be avoided. 



As an instance of a similar problem 

 the following may be quoted. In a cer- 

 tain glue factory it was found that the 

 glue turned black ; and its value was 

 seriously reduced, not only because of 

 the undesirable colour, but also because 

 its setting power was diminished. This 

 was found to be due to a bacterium 

 which excreted a black pigment. The 

 source of infection was discovered in a 

 dirty pipe previously used for the con- 

 veyance of ditch water, and afterwards 

 for delivering the finished glue into the 

 setting pans. When this pipe was 

 cleansed the evil disappeared entirely. 

 In such cases, the removal of the source 



* Since the above was written, I have been 

 informed that this blackening has reappeared. 



