From ancient times to the present, mankind has experienced many infectious diseases, which have mutually affected the development of society and medicine. In this paper, we review various historical and current infectious diseases in a five-period scheme of medical history newly proposed in this paper: (1) Classical Western medicine pioneered by Hippocrates and Galen without the concept of infectious diseases (ancient times to 15th century); (2) traditional Western medicine expanded by the publication of printed medical books and organized medical education (16th to 18th century); (3) early modern medicine transformed by scientific research, including the discovery of pathogenic bacteria (19th century); (4) late modern medicine, suppressing bacterial infectious diseases by antibiotics and elucidating DNA structure as a basis of genetics and molecular biology (20th century, prior to the 1980s); and (5) exact medicine saving human life by in vivo visualization and scientifically verified measures (after the 1990s). The historical perspectives that these five periods provide help us to appreciate ongoing medical issues, such as the present COVID-19 pandemic in particular, and remind us of the tremendous development that medicine and medical treatment have undergone over the years.

The hamstring muscles were analyzed anatomically and physiologically to clarify the specific reasons for the incidence of muscle strain of the hamstrings. For the anatomical study, hamstring muscles of 13 embalmed cadavers were dissected. For the physiological study, the knee flexor torque and surface electromyographic (EMG) signals were measured during isometric contraction of hamstring muscles in 10 healthy adults. The biceps femoris muscle long head (BF-L) and semimembranosus muscle (SM) had hemi-pennate architecture and their fiber length per total muscle length (FL/TML) was smaller than that of semtendinosus muscle (ST) and biceps femoris muscle short head (BF-S) with other architecture. The decrease of total muscle length per fiber length (ΔTML/FL) was larger in BF-L and SM than in ST and BF-S. The EMG activities at 0° of knee angle were at maximal compared with other knee angles and were of similar level in BF-L, in SM and in ST, whereas they were considerably smaller in BF-S. The EMG at 0° of knee angle activity per physiological cross-sectional area (PCSA) was about 1.6 times greater in BF-L than in SM. These results indicate the highest risk of muscle strain was in BF-L followed by SM.

The microcirculation is a major topic in current physiology textbooks and is frequently explained with schematics including the precapillary sphincters and metarterioles. We re-evaluated the validity and applicability of the concepts precapillary sphincters and metarterioles by reviewing the historical context in which they were developed in physiology textbooks. The studies by Zweifach up until the 1950s revealed the unique features of the mesenteric microcirculation, illustrated with impressive schematics of the microcirculation with metarterioles and precapillary sphincters. Fulton, Guyton and other authors introduced or mimicked these schematics in their physiology textbooks as representative of the microcirculation in general. However, morphological and physiological studies have revealed that the microcirculation in the other organs and tissues contains no metarterioles or precapillary sphincters. The metarterioles and precapillary sphincters were not universal components of the microcirculation in general, but unique features of the mesenteric microcirculation.

The structural and functional differences of individual hamstrings have not been sufficiently evaluated. This study aimed to clarify the morphological architecture of the hamstrings including the superficial tendons in detail using isolated muscle specimens, together with quantification of structural parameters of the muscle. Sixteen lower limbs of human cadavers were used in this study. The semimembranosus (SM), semitendinosus (ST), biceps femoris long head (BFlh), and biceps femoris short head (BFsh) were dissected from cadavers to prepare isolated muscle specimens. Structural parameters, including muscle volume, muscle length, fiber length, sarcomere length, pennation angle, and physiological cross‐sectional area (PCSA) were measured. In addition, the proximal and distal attachment areas of the muscle fibers were measured, and the proximal/distal area ratio was calculated. The SM, ST, and BFlh were spindle‐shaped with the superficial origin and insertion tendons on the muscle surface, and the BFsh was quadrate with direct attachment to the skeleton and BFlh tendon. The muscle architecture was pennate in the four muscles. The four hamstrings possessed either of two types of structural parameters, one with shorter fiber length and larger PCSA, as in the SM and BFlh, and the other with longer fiber length and smaller PCSA, as in the ST and BFsh. Sarcomere length was unique in each of the four hamstrings, and thus the fiber length was suitably normalized using the average sarcomere length for each, instead of uniform length of 2.7 μm. The proximal/distal area ratio was even in the SM, large in the ST, and small in the BFsh and BFlh. This study clarified that the superficial origin and insertion tendons are critical determinants of the unique internal structure and structural parameters representing the functional properties of the hamstring muscles.