Il6 THE AMOEBAE LIVING IN MAN 



of the shapes commonly met with. Oval or spherical cysts usually 

 measure about 9 /a to 12 /a in diameter : but it is extremely difficult to 

 state the dimensions of the more irregular forms even approximately. 

 Attempts to measure the more regular cysts have shown that their 

 commonest size is about 9-10 yu, in width by 10-12 yu, in length. I have 

 generally found that the simplest way to gauge the size of these cysts, in 

 practice, is to measure their greatest length and their greatest width, and 

 then take the mean as the " size " of the cyst. If this is done for a 

 number of specimens it will usually be found that the average " size " lies 

 between 10 /a and 11 fju. Cysts of all sizes from about 6yu, to 16 /j, occur, 

 however, but those with such extreme dimensions are uncommon. 



The living cysts have a fairly thick wall. They are of a clear white 

 colour, and usually contain two clearly visible inclusions — a number of 

 very brightly refractile granules, and a dull area of variable size, and 

 usually of a more or less spherical shape. The granules may be few or 

 many, collected together or dispersed through the cyst. They resemble 

 micrococci, and range in diameter from 0*25 yu, or even less up to about 

 I/*. After fixation they take up nuclear stains, but give them up on extrac- 

 tion more readily than the chromatin in the nuclei, and then readily 

 stain with plasma stains. They may show metachromatic staining (red) 

 with methylene blue or haematoxylin, but their reactions are difficult to 

 study on account of the impermeability of the living cysts to most stain- 

 ing reagents. Neutral red, when it can be got to enter the cyst, colours 

 them bright red ; but as a rule the contents of fully-formed cysts remain 

 quite colourless in watery solutions of this stain. The bright granules 

 do not stain with Best's carmine, and as a rule stain feebly with borax 

 carmine or paracarmine. They are insoluble in water, alcohol, chloro- 

 form, acetic acid, and most ordinary reagents. It appears to me pro- 

 bable, therefore, that they are not chromatin granules, and that they are 

 chemically different from the chromatoid bodies or granules in the cysts 

 of the Entanioehae. They seem, on the other hand, to consist of a sub- 

 stance similar to volutin, and I shall therefore speak of them as volutin 

 granules for the present. They are shown in the cysts figured in PI. I, 

 fig. II, and PI. II, figs, 38, 40-42. They have been omitted, however, 

 from the cysts outlined in Text-fig. 2. 



The dull inclusion in the living cysts of /. biitschlii is very strikingly 

 stained when they are placed in an aqueous solution of iodine. It then 

 assumes a dark mahogany colour, and appears as a solid body with a 

 well-defined outline. (See text-fig. 2, A to O.) This reaction at once 

 suggests that the inclusion is a mass of glycogen ; and this is confirmed 

 by its equally well-marked reaction when treated with Best's specific 

 carmine stain for this substance (fig. 39, PI. II). It is, moreover, insoluble 

 in alcohol and chloroform, but readily soluble in water ; so that in cysts 

 stained in watery solutions — such as iron-haematoxylin or haemalum — it 

 is completely extracted, and its place is represented by a vacuole (cf. figs. 

 40-42, PI. II). This glycogen mass is, of course, the structure which 

 Wenyon has termed the "iodophilic body," and from which he named 

 the cysts " Iodine cysts." It is doubtless homologous with the similar 

 glycogen masses or vacuoles found in the cysts of E. coli, E. histolytica, 

 E. nana, and other protozoa. 



The glycogen masses in the cysts of /. hiitschlii are most readily 

 studied in cysts suspended in iodine solution. (See text-fig. 2, A to O.) 

 They may be very small (fig. 2 F) or even absent (fig. 2 B), very large 



