tended to validate Virchow's opinion in this regard. Some of the gen- 

 eral contributions of cytology may be outlined as follows: 



Diagnosis: Many disease syndromes are, at least in part, diagnosed 

 on the basis of cellular change. Such changes include ( 1 ) shifts in rela- 

 tive frequencies of different types of cells, as in haemopoetic tissues and 

 peripheral blood; (2) changes in the morphology of particular kinds of 

 cells, or of granular inclusions, as in nerve cells; and (3) appearance of 

 cells and cellular debris in body fluids, used frequently as an aid to 

 diagnosis of special kinds of cancer. More recently, two kinds of diag- 

 nostic procedures involving chromosomal material have become impor- 

 tant. One is the use of the so-called "sex chromatin" test for diagnosis 

 of the genetic sex of individuals showing various degrees of sexual 

 dysgenesis. In this test, usually carried out on skin biopses or oral 

 smears, the genetic sex is considered female if 50 per cent or more of 

 the somatic nuclei show a single heteropycnotic chromatin mass near the 

 nuclear boundary (Nelson, 1958). The other new procedure correlates 

 change in karyotype with specific syndromes (Ford, 1960). For exam- 

 ple, at least 19 cases of Mongolism have all shown an extra chromosome 

 presumably representing a trisomic condition. When such correlations 

 become better established, human cytogenetics bids well to play a rather 

 direct role in certain kinds of diagnosis. 



Cancer: The problem of neoplastic growth may be considered to be 

 essentially a problem in applied cytophysiology. Cancerous or tumerous 

 growths, regardless of apparent cause or of whether they occur in plants 

 or animals, have one thing in common, namely, replication of cells with- 

 out organization or tissue function. This means that fundamental studies 

 on the physiochemical mechanisms involved in the normal mitotic cycle 

 are of direct concern, for until we fully understand the conditions under 

 which cellular replication occurs in normal tissue, we are not very likely 

 to obtain any real understanding of the situation in neoplastic growth. 

 Whatever attributes a cancer cell possesses or does not possess, it is cer- 

 tainly able to perform all functions leading to capability of undergoing 

 mitosis. 



Most theories of neoplastic induction are based on the general idea of 

 some specific alteration in a normal cell which eliminates its capacity to 

 integrate into a tissue, but which either increases or at least does not 

 impair its capacity to undergo replication. To date, the nature of these 

 proposed alterations is not known, though many causal agents such as 

 viruses, chemicals, radiation, and other physical stimuli have been dem- 

 onstrated. Two general theories have received most attention, i.e., somatic 

 mutation and virus infection. These two ideas are not necessarily mu- 



272 / CHAPTER 12 



