814 SUMMARY OF CURRENT RESEARCHES RELATING TO 



moro or less covered by a scum of Euglense, which is of a bright 

 brick-red colour in tho morning, and of a vivid green in the evening, 

 and which is much less conspicuous and defined during the day than 

 it is from sunset to sunrise. These variations in its characters aro 

 dependent on recurrent periodic changes in the condition of the com- 

 ponent Euglense. The definition, and specially the dry dusty aspect 

 of tho scum in the evening and early morning, are due to the fact 

 that at these times the vast majority of tho Euglense are aerial, and 

 not aquatic, organisms, the cells containing the then encysted and 

 passive protoplasts being raised in various degrees above tho surface 

 of the water, and in the majority of cases being entirely removed 

 from contact with it, and projecting freely into the air. Tho relative 

 inconspicuousness during the day is, on the other hand, due to tho 

 fact that they are then submerged, and swimming free in the water. 

 The changes in colour are dependent on alterations in the rclativo 

 amounts of red oily colouring matter, and especially in alterations in 

 its distribution within the bodies of the protoplasts. 



Tho scum is not, however, solely composed of Euglense, but, on 

 the contrary, contains masses of the empty cysts and stems with 

 dilated bases belonging to previous cycles of the encysted condition 

 of the organisms. Bright dry weather tends to induce constantly 

 increasing thickness in this scum, due to the fact that under such cir- 

 cumstances the normal cycle of developmental changes of form goes 

 on recurring with unbroken regularity, and that accordingly, quite 

 apart from coincident processes of multiplication connected with the 

 encysted condition of the organisms, there is necessarily a constantly 

 recurrent addition of increments of dead matter in the form of empty 

 cysts and stems. Heavy downfalls of rain, on the other hand, tend to 

 cause it to disappear, due to the fact that they both break up the sheets 

 of empty cysts and stems, and by driving the Euglense down into tho 

 water tend to prevent their normal assumption of an aerial habit. So 

 long, however, as conditions remain favourable to the regular periodic 

 succession of the diurnal and nocturnal phases in the life-history of 

 the Euglense, a steady increase in the scum goes on. Any scum 

 of this nature, composed in considerable proportion of dead organic 

 materials, affords a favourable site for the development of both sapro- 

 phytic and parasitic organisms, and we accordingly find it crowded 

 with infusorial, monadinic, and schizomycete forms. Among tho 

 latter curved forms are frequently and, under certain conditions, 

 apparently normally present in very large numbers. 



Dr. Cunningham goes on to show how " comma bacilli " can be 

 obtained with certainty, and in large quantity, by taking a mass of 

 this scum and introducing it into a glass of water. The Euglense die 

 off, and a scum accumulates composed of their bodies, empty cysts 

 and stems, sometimes to the depth of a quarter of an inch ; curved 

 schizomycetes, precisely resembling in their morphological characters 

 those found in choleraic media, crowd the under surface of the scum. 

 In two cases Dr. Cunningham succeeded in developing distinct 

 commas in cultivations where the scum material was used with feebly 

 alkaline agar- agar jelly. 



