To solve this problem, we need to understand the concept of muscle contraction and the lack of relaxation between successive stimuli.$\newline \bullet$When a muscle receives rapid stimuli without time to relax, it leads to a sustained contraction.$\newline \bullet$This phenomenon is known as tetanus.$\newline \bullet$In tetanus, the muscle remains in a continuous state of contraction due to the high frequency of stimuli.$\newline$Let's analyze the options:$\newline \bullet$Option 1: Spasm - A spasm is a sudden, involuntary contraction of a muscle or group of muscles. It is not related to sustained contraction due to lack of relaxation.$\newline \bullet$Option 2: Fatigue - Fatigue refers to the decline in ability of a muscle to generate force, often due to prolonged activity. It is not related to lack of relaxation between stimuli.$\newline \bullet$Option 3: Tetanus - This is the correct term for sustained muscle contraction without relaxation between stimuli.$\newline \bullet$Option 4: Tonus - Tonus refers to the normal, continuous state of partial contraction in resting muscles. It is not related to lack of relaxation between stimuli.$\newline$Therefore, the correct answer is Option 3: Tetanus.