NORMALITY, MICROSCOPIC 



233 



NORMALITY, MICROSCOPIC 



of blood in males differs from that in 

 females. And there are qualitative 

 differences in the primary and second- 

 ary sex organs. Consequently, as be- 

 tween races, so also as between the 

 sexes what is normal for one is not 

 necessarily normal for the other. One 

 must alwaj's bear in mind many known 

 differences and the likelihood of almost 

 innumerable others. 



Though a basic similarity exists in 

 the structure and function of the body 

 at all ages in the life of a given indi- 

 vidual, some very profound differences 

 clearly obtain, as between different 

 ages. What is normal for individuals 

 of the same race and sex, at, say, age 

 10 is clearly not normal at age twentj', 

 or at age fifty. It has been said that 

 the boy is not a little man and the 

 senile is not an old boy; he is a different 

 individual but he is constructed in the 

 same general pattern. 



No assessment of normality is there- 

 fore of any value unless the group is 

 homogeneous in race, sex and age. 

 Even this qualification is only sufficient 

 for a few properties relating to the body 

 as a whole such as weight, height, basal 

 metabolism, urinary excretion and so 

 on. 



The body is made up of so many parts 

 that it is frequently essential to con- 

 sider the normality of each separately 

 maintaining this homogeneity in race, 

 sex and age of the persons having the 

 parts compared. In the vascular sys- 

 tem the coronary artery ages much more 

 rapidly than the radial artery. Struc- 

 ture normal, or usual, for the coronary 

 artery at thirty is normal for the radial 

 at about sixty. The skin of the face 

 and hands ages more rapidly than that 

 in less exposed situations as for example 

 the back. What is normal for one at 

 age sixty is definitely not normal for 

 the other. 



To be on the safe side still other pre- 

 cautions are indicated. The method 

 employed to determine the normality 

 of the particular property in question 

 should be given, because some other 

 technique might yield higher or lower 

 values. One must also be on the look- 

 out for modifjnng conditions which 

 should be identified and specified. 

 Thus the normal secretory activity of 

 the sweat glands is modified consider- 

 ably by changes in the weather. When 

 temperature and humidity are high 

 during the summer, the level of normal 

 activity is different from that in the 

 winter. What is normal at high alti- 

 tudes is frequently not normal for parts, 

 or functional mechanisms, of indi- 

 viduals of the same race, sex and age 



measured by the same methods at sea 

 level. To further multiply examples 

 would be wearisome. 



Errors in Estimation: Histologists, 

 who would provide a sound basis for 

 work in pathology, should bear in mind 

 the considerations already mentioned 

 and others incident on the very in- 

 adequate techniques they employ. 



Before attempting to catalogue them, 

 however, it should be freely admitted 

 that, even in the best textbooks, there 

 is a deplorable looseness in descriptions 

 intended to convey information on the 

 normal microscopic structure of the 

 human body. Illustrations of human 

 tissues are often presented without 

 any qualifying data concerning them 

 and others of the tissues of a wide range 

 of lower animals are supplied, likewise 

 without qualifying data, the assump- 

 tion being made, all too frequently, 

 that they are truly representative of 

 normal human tissues. In many cases 

 they are representative and serve the 

 purpose. And it hardly needs to be 

 said, that for accurate and controlled 

 experiments animal tissues are essen- 

 tial. But it is not difficult to cite cases 

 in which examination of normal animal 

 tissues could convey a misleading idea 

 of normal human tissues of the same 

 kind. Kurloff bodies are a normal 

 component of the spleens of guinea 

 pigs, but not of human beings. The 

 demarkation of hepatic lobules by con- 

 nective tissue is notably characteristic 

 of certain species. What is normal in 

 this respect for the domestic pig is not 

 normal for man. 



Appearance in microscopic prepara- 

 tions of any kind may be technical 

 artifacts and may not indicate any de- 

 viation from normal in the tissue or 

 organ from which the preparation has 

 been made. The term artifact is de- 

 rived from L. ars, art and/aciw.'?, made. 

 It is something made artificially. 

 Webster defines an artifact as being 

 "in histology, a structure or appearance 

 in a tissue or cell due to death or to 

 the use of reagents and not present 

 during life." The degree of artifact 

 is proportional to the difference be- 

 tween the structure existing normally 

 in the living body and the structure ob- 

 served in the preparation. Details 

 are given in Laboratory Technique. 



In the case of living tissues, observed 

 with blood and nerve supply intact, 

 there is a possibility of artifact. It is 

 at a minimum in the rabbit ear cham- 

 bers, in which the ingrowing tissue is 

 very thin and can be studied with high 

 magnifications, and rather more to be 

 reckoned with when tissues must be 



