R. A. Fisher and his advocacy of randomization

The requirement of randomization in experimental design was first stated by R. A. Fisher, statistician and geneticist, in 1925 in his book Statistical Methods for Research Workers. Earlier designs were systematic and involved the judgment of the experimenter; this led to possible bias and inaccurate interpretation of the data. Fisher’s dictum was that randomization eliminates bias and permits a valid test of significance. Randomization in experimenting had been used by Charles Sanders Peirce in 1885 but the practice was not continued. Fisher developed his concepts of randomizing as he considered the mathematics of small samples, in discussions with “Student,” William Sealy Gosset. Fisher published extensively. His principles of experimental design were spread worldwide by the many “voluntary workers” who came from other institutions to Rothamsted Agricultural Station in England to learn Fisher’s methods.     

N. I. Vavilov-the man and his work

A brief sketch is presented of Vavilov's career, his main contributions to science and personal qualities. The imporatnce of his work in genetics, agro-ecology, plant breeding, the experimental taxonomy of crop plants and genetic resources conservation is also emphasized.     

Roles of his205, his296, his303 and Asp259 in catalysis by NAD+-specific D-lactate dehydrogenase.

The role of three histidine residues (His205, His296 and His303) and Asp259, important for the catalysis of NAD+-specific D-lactate dehydrogenase, was investigated using site-directed mutagenesis. None of these residues is presumed to be involved in coenzyme binding because Km for NADH remained essentially unchanged for all the mutant enzymes. Replacement of His205 with lysine resulted in a 125-fold reduction in kcat and a slight lowering of the Km value for pyruvate. D259N mutant showed a 56-fold reduction in kcat and a fivefold lowering of Km. The enzymatic activity profile shifted towards acidic pH by approximately 2 units. The H303K mutation produced no significant change in kcat values, although Km for pyruvate increased fourfold. Substitution of His296 with lysine produced no significant change in kcat values or in Km for substrate. The results obtained suggest that His205 and Asp259 play an important role in catalysis, whereas His303 does not. This corroborates structural information available for some members of the D-specific dehydrogenases family. The catalytic His296, proposed from structural studies to be the active site acid/base catalyst, is not invariant. Its function can be accomplished by lysine and this has significant implications for the enzymatic mechanism.     

The birth of immunology. II. Metchnikoff and his critics

The presentation of the phagocytic theory of immunity, proposed by Metchnikoff in 1883, was immediately attacked by German pathologists and microbiologists. Led by Baumgarten and Ziegler, criticism was levied against the hypothesis in three general respects: 1) Can an analogy truly be established between leukocyte phagocytosis and feeding of monocellular organisms? 2) What is compelling about the phagocytic process as a universal defensive activity? 3) General philosophic objections were raised, centered upon the accusation of a teleologic formulation. Underlying the argument was the rejection of the notion that the response of phagocytic leukocytes was truly causal in the successful response to infection. We note that the humoral school of immunity was not established until 1888-1890, and the early debate between Metchnikoff and his detractors was not over an alternative theory of an active immune response. There was none. With the development of the humoralist position, in direct response to Metchnikoff's formulation, a true dialogue about immunity, in the modern context of active host response, was initiated. The debate at this point changed to issues of mechanism (cellular versus humoral effectors), and the relative importance of defining innate versus acquired immune processes. Our study traces the scientific and logical basis of the initial rejection of the phagocytosis theory. More broadly, the analysis of this debate elucidates the emergence of a new concept of immunity that rested upon the notion of an active host response. The humoralists erected their theory on Metchnikoff's original scaffold, and the ensuing debate of the nascent science relied on the successful establishment of his basic concept. With the studies of Bordet, Metchnikoff's protégé, the essential resolution of the acrimonious debate was offered. Metchnikoff continued his research by attempting to apply the phagocytosis theory to mechanisms of senility, while immunology oriented itself toward the biochemical definition of immune recognition.