ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 



991 



minute forms may be equally great; but, even if we confine our 

 attention to those observed, we cannot but conclude that their effect 

 in removing organic matter must be very considerable ; and judging 

 from what occurs in the case of larger animals, those 1/1000 of an 

 inch in diameter may well be supposed to consume as food, particles 

 of the size of germs. Up to the present time, I have, however, 

 collected so few facts bearing on this question, that it must, be re- 

 garded merely as a suggestion for future inquiry. 



So far, I have referred exclusively to the effect of animal life. 

 Minute plants play an important part in another way. The number 

 per gallon of suspended diatoms, desmids, and confervoid alga) is, in 

 some cases, most astonishing, and they must often produce much 

 more effect than the larger plants. As far as I have been able to 

 ascertain, their number is to some extent related to the amount ot 

 material in the water suitable for their assimilation and growth. In 

 the mud deposited from pure rivers their number is relatively small, 

 but in the district of the Thames, where the sewage is discharged, I 

 found that in smnmer their number per grain of mud at half-ebb tide 

 was about 400,000, which is equivalent to above 5,000,000 per gallon 

 of water. This is two or three times as many as higher up or lower 

 down the river, and, out of all proportion, more than in the case of 

 fairly pure rivers like the Medway. Their effect in oxygenating the 

 water must be very important, since, when exposed to the light, they 

 would decompose carbonic acid and give off oxygen, under circum- 

 stances most favourable for supplying the needs of animal life, and 

 counteracting the putrefactive decomposition so soon set up by minute 

 fungi when oxygen is absent. 



Taking then, all the above facts into consideration, it appears to 

 me that the removal of impurities from rivers is more a biological 

 than a chemical question ; and that in all discussions of the subject, 

 it is most important to consider the action of minute animals and 

 plants, which may be looked upon as being indirectly most powerful 

 chemical reagents." 



Examination of Handwriting.* — Dr. G. E. Fell records a 

 curious case in which the Microscope was applied by himself and 

 Prof. D. S. Kellicott to the detection of the manipulation of a written 

 document. , 



At first sight the document looked as if it was all written with 

 one kind of ink — a heavy black ink. Closer examination with a 

 Microscope, however, showed that the original writing was in a pale 

 yellow ink, and that this had afterwards been traced over with the 

 black ink. Further examination showed that the last clause, " And 

 Colby's bond is hereby cancelled," had been originally written with 

 ink of a brownish tinge. The document was held by the judge, before 

 whom tlie case came, to be spurious, the inference being that the 

 words quoted above had been added after it was signed, and that then 

 the wh(jle was traced over in order to make the entire document 

 ai)pear to have been written at one time and with tho same ink. 



♦ I'roc. Amor. Soc. Micr., 7th Ann. Meeting, 1881, pp. IT-SS. 



