Table 1. — Advantages and disadvantages of various methods that have been used to study blood 



cells — Continued 



Method of study 

 3. Dry fixed smears. 



A thin smear of blood or other tissue 

 cells on a slide, dried in the air, 

 stained, and dried again after stain- 

 ing. 



Advantaiies 

 maxinnim slriietnral and tine- 

 ihat permit differentia- 



1. Reveal 



torial gradation 



tion hetween closely similar cells 



2. Easy to prepare. A technic useful for 

 work in field or laboratory research. Mini- 

 mum equipment and time required. 



Disadvantages 

 1. Lose topcgrajihic relations with other 

 cells and tissues. 



2. Because cells in dry smears appear struc- 

 turally different from cells in fixed-tissue 

 preparations, they cannot be readily com- 

 pared with cells in fixed tissues. 



4. Electron microscopy. 



Spread cells on a gelatin screen and 

 place in a vacuum chamber of the 

 apparatus. Killed cells sometimes 

 jireviously treated >vith osmic acid 

 or other metals. 



1. Offers higher magnification and resolving 

 power than any previous method. Its 

 greatest usefulness is to make visible minute 

 structural details within the cell. 



1. It is necessary, not only to kill the cells, 

 but also to dehydrate them cftmpletely in 

 vacuum, thus removing all volatile mole- 

 cules. 



2. This treatment of tissue cells may pro- 

 duce distortions even greater than those 

 that occur in the usual fixed and stained 

 preparations. 



3. Staining technics thus far are limiled to 

 the use of metallic stains. 



4. In order to see most cells with the electron 

 microscope, the material needs to be cut 

 into sections thinner than one micron. 



LIVING CELLS 



L Living cells are generally tlioiighl lo give 

 a better stantlarfl for measuring reality of 

 structures than do killed and stained cells. 



2. Measurements of size are more accu- 

 rately made on live than on dead cells. 



1. The perception ol the cell and its internal 

 structure is dependent ii|)on differences in 

 refractive indices. Therefore, the fact that 

 an object catinol be seen \\ilhin a living cell 

 is not pniof that the object's j>resence in 

 killed and stained cell is an artifact. 



A. In vim methods. 



.\ll technics where cells are studied 

 within the body, such as the blood 

 studies made on the living tadpole 

 tail, the transparent chamber built 

 in the rabbit ear, and the use of the 

 quartz tube to concentrate light for 

 the study of vascidar problems in 

 (he internal organs. 



L Study of cells in their nalnral location 

 within the body bathed by normal body 

 fluids gives the most reliable informalion 

 of any method. That w bicli can be clearly 

 seen may" he regarded with considerable as- 

 surance as a true picture. 



2. The same cell can be followed over a con- 

 si<lerable period in all of its reactions to sur- 

 rounding cells of the body. \ aluable in 

 folloning the Iransformalion of an indi- 

 vidual cell from one type into another. 



L Technic difficulties are often insurmount- 

 able. Low-power studies have their useful- 

 ness, but individual cells are scarcely visible. 

 L'se of water or oil immersion lenses means 

 a short working distance with all its limita- 

 tions. 



2. It is often difficidt lo transmit enough 

 light through the tissues to ilhnuinale ade- 

 quately the field for high power work. 



3. Sometimes light itself, even free from 

 heat, will disturb the normal j)hvsiologv of 

 cells. 



4. Often an operation is required to see the 

 cells and this introdiues a disturbing factor. 



B. In vitro methods. 



Tissue cidture chiefly', but it in- 

 cludes, also, all technics where li\ ing 

 cells are studied outside the IxkIv. 



1. Cells taken outside the body can be sub- 

 jected to a witler variety of technical 



1. Cells removed from the body are no 

 longer boimd by the same physical and 



methods, and the cells can be followed more chemical environmental forces that existed 

 closely than within the body. inside the body, and new equilibriums are set 



up that may lie atvjiical. 



2. In temporary moinits expected to last for 

 merely a mailer of hours, the cells begin 

 their degenerative jirocess as soon as they 

 leave the body, and it becomes difficult to 

 determine between the extremes of normal 

 variability and the early stages of irreversible 

 degeneration. 



