FALLACIES AND PUZZLES IN BLOOD EXAMINATION 113 



case like this a careful search of the film helps one to a decision, if not to a diagnosis, for 

 it should always be remembered that a i^arasitic blood infection is usually multiple, that 

 is to say, that it is rare to find only one example of a true blood parasite in any given 

 film. This may occur, especially as regards malarial crescents and filariae, but if we think 

 we have found a new and peculiar hsematozoon, and yet can only discover a solitary 

 example of it in, say, two good-sized and well-made blood films, it is well to pass into a 

 mood of combined reflection and doubt. Wherever possible, also, it is advisable, as Daniels 

 says, to examine some part of a slide where the stain has extended beyond the blood 

 film and see if the same appeai'ances are there. Another point worth noting is that 

 in Australia the spermatozoa of birds (honey-eaters) were at first mistaken for spirochetes 

 in the blood, as the long and narrow types show regular spiral curves. The shot wound 

 had apparently injured the spermatic duct and permitted spermatozoa to pass into the 

 blood clot. 



Eeturning to our yeast cells we find they present very varying forms. A glance at 

 Plate XIV., fig. fj, in our Second Report will show a torula from the stomach of a jerboa 

 which, under certain conditions, might quite possibly deceive the very elect, while 

 reference to paije 205 in this Eeport will show what I believe to be another form of 

 yeast cell which was associated with a cutaneous Leishmaniosis, and led more than 

 one person who saw it, astray. 



How easy it is to fall into what we may perhaps call the yeast trap is shown by the 

 amount of literature which has accumulated on the pai-asite of epizootic lymphangitis. 

 This has been definitely shown to be a yeast, and has been cultivated as a fungus growth 

 on artificial media, and yet many able observers have considered it to be a protozoon 

 allied to the Leishmania or Leucocj"tozoa. 



What then will guide us in distinguishing a stained yeast cell from a blood parasite ? How to dis- 

 Apart from the historv of the film and the general shape and appearance of the veasts, one ""S"'^^ y^^' 

 notices that those portions of their cytoplasm which take on the chromatin hue, stain a parasites 

 very intense ruby-red, and that they are also, as a rule, more compact and " solid '' looking 

 than the nucleus or blepharoplast of a liEematozoon. The appearance of the capsule 

 may help, as witness the well-known double contour of the Saccharomyces farciminosus, 

 to adopt Eivolta's name for the parasite of epizootic Ijinphangitis. In some cases, however, 

 the only thing to be done is to make a careful drawing and record the find with such 

 particulars as may help, especially making mention of any other forms — bacilli, cocci, 

 etc., which may indicate contamination (i-ide Plate VII., fig. 10). 



After all, a little experience and careful reasoning will usually prevent mistakes in the 

 case of Class I., but mention must be made of another and most important fallacj\ It 

 is, or has been, until recently, a common custom to dry a stained blood film, after washing, 

 by means of blotting paper. What is often done, is to have a bunch of pieces, of paper, 

 to lift some of them up exposing the surface of one, place the slide on this and blot the 

 film with those held in the hand. Now, unless care be taken to see that the piece of 

 filter paper, whose under-surface is pressed down upon the film, is of virgin purity, 

 disaster may ensue. I remember telling my laboratory attendant to prepare for trans- 

 mission to India a number of films of mammalian blood showing hiEmogregarine 

 infection. Happily, I bethought me to look them over before despatch. I speedily 

 found they contained oval and nucleated red cells w-hich must have come from a bird 

 or a reptile. Despite denials, I came to the conclusion that either the slides, the 

 pipettes or the spreading needle used had been dirty. It was not until a somewhat 

 similar episode occurred in the course of my own work that I realised what had 



